IIO FOSSIL ECHIDNAS CHAP. 
many other mammals.” In Hehidna, too, but not in Ornitho- 
rhynchus, the hemispheres are well convoluted, though the arrange- 
ment of these convolutions cannot be brought into line with what is 
known concerning the convolutions upon the hemispheres of other 
mammals. It had been stated that in these animals, at least in 
Echidna, there were only two optic lobes, as in lower vertebrates, 
instead of the mammalian four. The late Sir W. H. Flower set 
this matter at rest,’ and showed that Hehidna was in this respect 
typically mammahan. The absence of the corpus callosum is 
one of the principal features separ- 
ating the Monotremes from other 
mammals. | 
The Monotremata are repre- 
sented to-day by two types, Ornitho- 
rhynchus and Echidna, which are 
no doubt worthy of being placed in 
separate families. Fossil remains 
of the group (apart from the prob- 
lematical Multituberculata) are only 
known from Pleistocene times in 
Australia, and consist of the bones 
of a large species of Hehidna, and 
: some fragments of Ornithorhynchus, 
Fic. 53.—Brain of Echidna aculeata, indicating a smaller animal than 
Parker aud Haswells Zoology.) ee living Platypus 
Fam. 1. Echidnidae.—This 
family contains two genera, of which Echidna is the older and 
much the better known. The skin is abundantly covered with 
spines, with which are mingled hairs. The snout is tapering, 
the tail rudimentary, and the fingers and toes five in number. 
The spur and gland upon the caleaneum are smaller than in 
Ornithorhynchus. ‘The claws are very strong, serving to tear 
open the ants’ nests, upon the inhabitants of which the Echidna 
feeds, licking them up with a long extensile tongue like that of 
Myrmecophaga. In relation to this habit the salivary glands are 
enormously developed, and indeed the animal has been con- 
founded with Myrmecophaga,* as the vernacular name “ Australian 
Anteater” exemplifies. 
1 Proe. Zool. Soc. 1864, p- 18. 
* Myrmecophaga aculeata was the name given by Shaw. 
